Koh Tachai is a remote Similan-area plateau dive built around granite boulders, coral gardens, and open-water current. The main route breaks into channels and ledges that reward controlled drifts when the water is moving, while the quieter pockets let you work the reef and sand patches. Divers come here for big schools of barracuda, trevally, and fusiliers, plus manta, whale shark, turtle, and ray chances when conditions line up.